Two-stage hydrogenation treatment for hydrocarbon oils



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Jan. 18, 1949.

, mit this operation to be Patented Jan. 18, 1949 OGENATION TREAT- TWO-STAGE HY DR MEN T FOR Warren M. Smith,

HYDROCARBON OILS Baton Rouge, La., assignor to Standard Oil DevelopmentCompany, a corporation of Delaware Application May 11, 1945, SerialNo.,593,124

3 Claims. 1

The object of my invention is to hydrogenate a hydrocarbon oil so as tosaturate aromatic hydrocarbons, and at the same time to hydrogenateoleflns, without causing cracking in any substantial degree.

As is known to those who are familiar with the petroleum art, andparticularly the catalytic cracking art, it becomes desirable tohydrogenate a hydrocarbon oil such as the gas oil remaining unconvertedfrom a cracking operation before it is recycled to the cracking zone.The reason it is necessary and/or desirable to hydrogenate this materialis that the arcmatics therein, particularly the aromatics containing twobenzene rings in a condensed nucleus, are extremely refractory towardsfurther cracking and possess a strong tendency to produce relativelylarge quantities of coke on the cracking catalyst when rerun through thecracking zone. It is also desirable to saturate olefins in the cycle oilfor substantially the same reason, namely, that the paraflins thusformed have a lesser propensity to form coke on the catalyst.

Heretofore and prior to my invention, although the commercialhydrogention of olefinic material has been achieved both at low and athigh hydrogen pressures with catalysts resistant to the deactivatingaction of such naturally occurring impurities as sulfurandnitrogen-containing compounds, the non-destructive hydrogenation ofaromatic materials to their corresponding naphthenic derivatives hasbeen successfully carried out only at high hydrogen pressure (200atmospheres) with similar type catalysts. The low pressure hydrogenationof these aromatic materials has been accomplished only with eX- cessiveloss in catalyst activity. Since these aromatic materials. when freedfrom the usual naturally occurring sulfurand nitrogen-containingcompounds, can be hydrogenated at low pressures without excessive lossin catalyst activity, the removal of these impurities willpersuccessfully carried out. Among the advantages of a low pressurehydrogenation process are the lower initial equipment cost per unit ofproduct obtained, the lower process cost for operation of saidequipment, and the simpler method of operation.

According to my present invention, the low pressure hydrogenation ofaromatic and olefinic type materials may be achieved without excessiveloss in catalyst activity with time by means of a two-stage process,wherein the first stage is operated with a sulfur-resistant catalyst atlow methods pressures and high temperatures for removal ofolefinicmaterials and sulfur and nitrogen while the second stage isoperated with the same type of catalyst or a sulfur-sensitive catalystat conditions similar to those of the first stage except at lowertemperatures for hydrogenation of arcmatic materials.

In the accompanying drawing, I have shown diagrammatically a suitablearrangement of apparatus elements in which a preferred modification ofmy-invention may be carried into practical elfect.

Referring in detail to the drawing, a gas introduced into the presentsystem through line I, and thence forced through a heating coil 3, whereit is heated to a cracking temperature and thereafter passed through thecatalytic cracking zone 5. Since my improvements go to special ofhydrogenating hydrocarbon oil rather than to cracking it, I shall onlyrefer to the cracking operation without describing it fully, for anycracking operation may be employed that is of the fixed bed or fluidtype of process using natural clay or synthetic catalyst, all of whichvarious types of cracking processes are known to petroleumtechnologists. In the diagram, the cracked products are withdrawn fromcracking zone 5 via line l0 and discharged into a fractionaldistillation tower I2 Where the oil is subjected to the usualdistillation process in a conventional plate tower to separate the crudehydrocarbon mixture into several cuts of distinct boiling ranges; thus,for example, normally gaseous and/or light ends may be taken 01?overhead through line while taken off through line 22. The products fromlines 20 and 22 may be processed further in equipment not shown torecover commercial products, according to known means.

Referring to the unconverted gas oil Whose treatment goes to the heartof my invention, a sample is withdrawn through line by pump and thencepassed to line 3| and through a heating coil 32 into a hydrogenationreactor containing a body of catalyst C which will be more fullyidentified hereinafter. ously, hydrogen and hydrogen-containing gas areintroduced into the system through lines and Si and mixed with the gasoil in line 3| before going to heating coil 32. In this first stage ofthe hydrogenation, the oil feed, which may contain sulfur compounds andnitrogen compounds and which definitely contains olefinic and aromaticmaterials, is saturated with respect to the olefinic oil is a gasolinefraction may be Simultanehydrocarbons; the product which is removed fromreactor 40 via line 42 and passed through cooler 4| and line 60 toliquid-gas separator 8| contains parafilnic and aromatic constituentswith greatly decreased quantities of sulfurand nitrogencontainingmaterial impurities. Hereinafter, I have set forth the operatingconditions such as catalysts, pressures, temperatures, feed rates. andgas rates to be employed in hydrogenator 40. Since the product inseparator 8! may contain some volatile nitrogen compounds and sulfurcompounds, it is desirable to pass the material to a scrubber 82 vialine 68 for the purpose of removing these compounds. The separator gaswhich has previously been washed in scrubber 83 is used to remove thesevolatile compounds from the product in scrubber 62, after which it isreturned to the hydrogenation system through line Alternatively,scrubber- 52 may be replaced by a conventional liquid phase washingsystem employing acid and caustic solutions for the removal of anynon-volatile nitrogen and sulfur compounds formed during thehydrogenation in reactor and not completely removable by gas blowing.The scrubbed product thence passes through line 52 to storage tank 53from which it is withdrawn by pump 54 and thereafter mixed with hydrogenand hydrogen-containing gas from lines 55 and 56 and passed to firedcoil 64 where it is reheated. The vaporized mixture is thence passedinto a second hydrogenation reactor 65, containing a body of catalyst C.The mixture of hydrogen and hydrocarbons passes through the reactor anda body of catalyst; during this passage through the catalyst, thearomatics are hydrogenated and thereafter the product issuing throughcooler 66 and line 10 to liquid-gas separator II is released to storagetank 12 from which it may be withdrawn by pump 13 and returned forfurther processing in cracking zone 5. The separator gas which is washedin scrubber I4 is returned to the hydrogenation system through line 56.

As to operating conditions, in the first or feed purification stage ofthe hydrogenation process, I propose to use a catalyst consisting ofsulfides of metallic elements of group VI or group VIII of the periodicsystem or mixtures of the same, either as such or supported on an inertcarrier which may be composed of alumina, silica, di-

atomaceous earth, and the like. As examples of the same may be mentionedmolybdenum sulfide on activated alumina, mixtures of nickel sulfide andtungsten sulfide or molybdenum sulfide, and so forth. The pressures forthis process are in the range of 200 to 1000 pounds per square inch withtemperatures of 500 to 900 F. and preferably from 700 to 900 F. Gasrates of 5000 to 10,000 cubic feet per barrel of feed or 10 to 20 molesof hydrogen per mole of feed are used with feed rates in the range offrom 0.5 to 4 volumes of feed per volume of catalyst per hour.

In the second or aromatics hydrogenation stage of my process, theconditions employed are similar to those used in the first stage, butthe temperatures are maintained somewhat lower, being of the order of300 to 700 F. The catalysts used in this second stage may be the same asthose used in the first stage or they may consist of supported metalsand/or metal oxides of group VIII elements of the periodic system. Asuitable material is metallic nickel on alumina, silica gel, kieselguhror similar carrier.

The following example may serve to illustrate Ill - Sulfur, WeightPercent...

certain oi the features of the hydrogenation process:

Feed Stock to Catalytic Cracking Virgin Paraillnic Gas Oil BoilingPoint, 50% F 570 Sullur Weight Percent 1.05 Specific Dispersion 129 11ydrogcnatcd Product Boiling Point, 50%

Specific Dispersion That the hydrogenated product is an improved feedstock for further catalytic cracking is indicated by the much lowerspecific dispersion. This property is indicative of a lower aromaticcontent as illustrated in the following tabulation showing the relationbetween the specific dispersion of hydrogenated catalytically crackedcycle stocks and their ease oi cracking as distinguished by their extentof cracking under the same given cracking conditions.

From this example it may be seen that hydrogenation of a catalyticallycracked cycle stock improves its catalytic cracking characteristics. Inaddition, as the extent of hydrogenation increases and the content ofrefractory aromatic material decreases, as indicated by the specificdispersion of the hydrogenated product, its ease of cracking increases.

In the foregoing example, it has been clearly shown that catalyticallycracked cycle stocks containing aromatic materials refractory towardsfurther catalytic cracking may be sufficiently improved in catalyticcracking characteristics by low pressure hydrogenation at therepresented operating conditions to be comparable with the virgin gasoil feed stock with respect-t0 ease of cracking. Continued successfuloperation at these conditions requires the use of a feed pretreatmentstep which may be achieved. at conditions similar to those in thearomatics hydrogenation step, but at an elevated temperature.

While I have described a two-stage hydrogenation process and used as anillustration the hydrogenation of a catalytically cracked cycle stock, Iwish it to be distinctly understood that the example which I havepreviously given, relating to the hydrogenation of a catalyticallycracked gas oil cycle stock, was purely illustrative and not given forthe purpose of imposing any limitation on my invention. My inventionapplies broadly to any process where it is desired to non-destructivelyhydrogenate a hydrocarbon oil to saturate the olefins contained therein,and to reduce the aromatics content by their hydrogenation tonaphthenes, regardless of the source of the oil or of the use to whichit may subsequently be put. I have described the nature and purpose ofmy invention in the best mode of carrying it into effect.

What I claim is:

1. A two-stage hydrogenation process which comprises feeding ahydrogen-containing gas and a gas oil containing aromatics, sulfur andnitrogen to a reaction zone maintained at a tempera ture of from 700 to900 F. under a pressure of from about 200 to 1000 pounds per squareinch, and containing a sulfactive catalyst selected from the groupconsisting of the sulfides of metals of groups VI and VIII of theperiodic system and mixtures of such sulfides, permitting the said gasoil to remain resident in the reaction zone for a suflicient period oftime to convert the nitrogen and sulfur compounds in the said feed stockto volatile compounds, withdrawing the reaction products from saidreaction zone, removing volatile nitrogen and sulfur compoundstherefrom, passing the substantially sulfur and nitrogen free product toa second reaction zone where it is contacted with hydrogen and asulfur-sensitive catalyst at temperatures of from 500 to 700 F. whileunder pressures of from about 200 to 1000 pounds per square inch for asufiicient period of time to effect simple hydrogenation of olefins andaromatics in the said oil, and recovering from the said second zone aproduct of lower aromaticity than the original feed stock, but havingsubstantially the same boiling range as the original feed stock. 1

2. A two-stage. hydrogenation process which comprises feeding ahydrogen-containing gas and a gas oil containing aromatics, sulfur andnitrogen to a reaction zone maintained at a temperature of from about700 to 900 F. under a pres sure of from about 200 to 1000 pounds persquare inch, and containing as catalyst a mixture of nickel and tungstensulfides, permitting the said gas oil to remain resident in the reactionzone for a sufllcient period of time to convert the nitrogen and sulfurcompounds in the said feed stock to volatile compounds, withdrawing thereaction products from said reaction zone, removing volatile nitrogenand sulfur compounds therefrom, passing the substantially sulfur andnitrogen free product to a second reaction zone where it is contactedwith hydrogen and a sulfur-sensitive catalyst at temperatures of fromabout 500 to 700 F. while under pressure of from about 200 to 1000pounds per square inch for a sufficient period of time to effect simplehydrogenation of olefins and aromatics in the said oil, and recoveringfrom the said second zone a product of lower aromaticity than theoriginal feed stock, but having substantially the same boiling range asthe orig inal feed stock.

3. A two-stage hydrogenation process which comprises feeding ahydrogen-containing gas and a gas oil containing aromatics, sulfur andnitrogen to a reaction zone maintained at a temperature of from 700 to900 F. under a pressure of from about 200 to 1000 pounds per square inchand containing as catalyst a mixture of nickel sulfide and molybdenumsulfide, permitting the said gas oil to remain resident in the reactionzone for a sufficient period of time to convert the nitrogen and sulfurcompounds in the said feed stock to volatile compounds, withdrawing thereaction products from said reaction zone, removing volatile nitrogenand sulfur compounds therefrom, passing the substantially sulfur andnitrogen free product to a second reaction zone where it is contactedwith hydrogen and a sulfur-sensitive catalyst at temperatures of fromabout 500 to 700 F. while under pressures of from about 200 to 1000pounds per square inch for a sufiicient period of time to eifect simplehydrogenation of olefins and aromatics in the said oil, and recoveringfrom the said second zone a product of lower aromaticity than theoriginal feed stock, but having substantially the same boiling range asthe original feed stock.

WARREN M. SMITH.

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